Log Message:
gnuplot: updated to 5.2.8

Changes in 5.2.8
* CHANGE user-visible GPVAL_TERM_HCHAR GPVAL_TERM_VCHAR (help debug font issues)
* CHANGE placement of ylabel (compromise 5.2.7 and earlier versions)
* CHANGE make strstrt() aware of UTF8, e.g. strstrt("αβγ5", \ 
"5") returns 4
* FIX "set timestamp" from "save" must not include a \ 
justification
* FIX set cntrparam levels increment <base>, <factor> for logscale z
* FIX character pointtypes should inherit plot coloring like normal pointtypes
* FIX bad autoscaling of linked y2 axis
* FIX prevent infinite loop from unbounded interation in a non-data plot command
* FIX dimensions reported by "stats matrix every"
* FIX extent of boxplot whiskers could be off by one point
* FIX mix unbounded iteration and functions in a single plot command
* FIX reverse history search with readline=builtin
* FIX qt: suppress off-by-one ysize
* FIX cairo: suppress off-by-one ysize
* FIX gd: apply alpha to brushstroke lines
* FIX tikz: fixes to accommodate lua 5.3 and newer pgf
* FIX wxt: ExportToFile widget disabled in persist mode
* FIX qt: handling of modifier keys (ctrl alt shift) for keyboard events
* FIX wxt: handling of modifier keys (ctrl alt shift) for keyboard events
* FIX fig: dashtype "solid" was not passed through correctly to transfig
* FIX gd: incorrect line spacing of multiline label